The cleanup plans required approval of the Planning Commission, but do not require any action by the Ann Arbor City Council.

The Planning Commission's approval is contingent on DTE obtaining variances from the city's Zoning Board of Appeals from providing a new stormwater management system, as well as obtaining permits from the DEQ. DTE also must provide the city with legal descriptions of water main and storm sewer easements before the city will issue grading permits.

The MichCon site cleanup plans were submitted to the city in conjunction with a site plan for a new electrical substation DTE wants to build across the street. Planning commissioners postponed action on the site plan for the substation at Tuesday's meeting.

DTE proposes to construct a new electrical substation at its service center facility at 984 Broadway St. to address increased demand for electric power in downtown Ann Arbor.

The substation addition would be located at the northeast corner of the site in an area now occupied by a service drive, according to a city staff report.

The substation would consist of two 15.5-foot tall electrical transformers and related electrical equipment on raised concrete pads and a new Power Delivery Center, a 630-square-foot, 12.5-foot-tall steel structure. The project also would include a new 6-foot-tall perimeter chain link fence with one foot of barb wire and a concrete block retaining wall.

The site is located in the 100-year floodplain of the Huron River. DTE proposes using 800 cubic yards of fill to construct the raised transformer pads. To mitigate the impact to the floodplain, it proposes removing 1,155 cubic yards of fill on the Michcon site.

The removal of a building on the MichCon site also provided an additional 55 cubic yards of storage capacity that DTE wants to count toward its floodplain mitigation efforts.

As part of the MichCon site cleanup, DTE plans to remove some of the most contaminated soil, replace it with clean fill, and construct a containment cap along the Huron River.

The work will require the removal of 33 landmark trees along the riverbank to excavate contaminated soil underneath them. DTE plans to plant 207 two-inch caliper replacement trees along the waterfront and adjacent the railroad embankment at the southwest corner of the site.

Some of the cleanup work will take place in the Huron River, where DTE will remove contaminated soil and construct two whitewater features for kayakers.

No new building construction is proposed as part of the project and no buildings exist on the site at this point.

Although some of the most heavily contaminated soils of the site will be removed, other less-contaminated portions will remain and not be remediated with this project, according to a staff report prepared by City Planner Jeff Kahan.

DTE has indicated that because contaminated soil will remain on the site after remediation, installing a new stormwater detention system would be harmful to groundwater and the Huron River. The plan is to keep the old parking lot and building foundations intact for now to provide a cap on top of the contaminated soils that will remain after this year's cleanup project.

According to Kahan's report, the Huron River was re-routed from its historic alignment through the middle of the MichCon site to its current location in 1915.

"The gasworks operation ended decades ago and MichCon removed many of the older structures and eventually replaced them with a service center in the middle to latter part of the 20th century," Kahan stated in the report. "Over the past few years, MichCon has removed all of the structures on the site. The access drive, parking lots, and building pads remain."

The cleanup is expected to take place from August through October. Ann Arbor officials are hoping to turn the site into a riverfront park eventually, while there also are talks of using a portion of the property to develop a riverfront restaurant and new office space.

Ryan J. Stanton covers government and politics for AnnArbor.com. Reach him at ryanstanton@annarbor.com or 734-623-2529. You also can follow him on Twitter or subscribe to AnnArbor.com's email newsletters.